The present invention relates to particles of stabilised peroxygenated compounds, a process for their manufacture, and compositions, possessing a bleaching action, which contain these particles.
It is well-known that certain peroxygenated compounds can be employed as bleaching agents in detergent mixtures in powder form. In the usual domestic detergent powders, it is customary to employ sodium perborate tetrahydrate as the bleaching compound because it is relatively stable to decomposition in a detergent medium. However, it is becoming more and more usual to employ cold washing and soaking techniques for laundry, and for these techniques sodium perborate suffers from the disadvantage of dissolving too slowly at 20.degree. C. To overcome this disadvantage, it has been proposed to introduce, into the detergent powders, other inorganic peroxygenated compounds, especially alkali metal percarbonates, perphosphates and peroxymonosulphates, which have suitable rates of dissolution.
Numerous processes have hitherto been proposed for manufacturing particles of these peroxygenated compounds, but in the majority of cases the particles obtained possess insufficient resistance to attrition, insufficient shelf life in a moist atmosphere or insufficient stability towards other constituents of the detergent powders. A valuable process for the manufacture of particles of sodium percarbonate, which makes it possible to overcome some of the disadvantages mentioned above, consists of introducing a solution of hydrogen peroxide and a solution of sodium carbonate into a fluidised bed containing seeds of a size smaller than those of the particles which it is desired to obtain (French Pat. No. 70/01,315 filed on Jan. 14, 1970 in the name of Solvay & Cie, published under No. 2,076,430). This process makes it possible to obtain particles which are much more resistant to abrasion than those obtained by other processes.
Furthermore, it has also been proposed (French Pat. No. 76/15,716 filed on May 20, 1976 in the name of Interox and published under No. 2,324,574), for the purpose of improving the stability of particles of peroxygenated compounds, to coat them by means of solid coating agents which contain sodium carbonate mixed with sodium silicate and either sodium sulphate or sodium bicarbonate. Though this technique makes is possible very substantially to increase the stability of the particles of peroxygenated compounds, the stability nevertheless remains less than that of the particles of sodium perborate tetrahydrate.